CONSERVATION LAW

also called Law Of Conservation, any of several principles applied in physics that state that certain physical properties (i.e., measurable quantities) do not change in the course of time within an isolated physical system. In classical physics, laws of this type govern mass, energy, momentum, and electric charge. In particle physics, other conservation laws apply to properties of subatomic particles that are invariant during interactions. Each such law signifies that nature remains constant with the passage of time. An important function of conservation laws is that they make it possible to predict the macroscopic behaviour of a system without having to consider the microscopic details of the course of a physical process or chemical reaction. Conservation of mass implies that matter can be neither created nor destroyedi.e., processes that change the physical or chemical properties of substances within an isolated system (such as conversion of a solid to a gas) leave the total mass unchanged. The special theory of relativity, however, has shown that mass and energy are equivalent, although interconversions of mass and energy are too small to be detectable except in cases involving subatomic particles or speeds comparable to that of light. In these situations, conservation of mass may be considered to be a special case of the more general law of conservation of mass-energy. Conservation of energy implies that energy can be neither created nor destroyed, although it can be changed from one form (mechanical, kinetic, chemical, etc.) into another. In an isolated system, the sum of all forms of energy therefore remains constant. For example, a falling body has a constant amount of energy, but the form of the energy changes from potential to kinetic. Again, if relativity is applicable, the more general law of conservation of mass-energy holds. Linear momentum is conserved in a system containing a number of moving bodies; that is to say, the total momentum (a vector quantity) of the system remains constant. Since momentum is conserved, its components in any direction will also be conserved. Application of the law of conservation of momentum is important in the solution of collision problems. The operation of rockets exemplifies the conservation of momentum: the increased forward momentum of the rocket is equal but opposite in sign to the momentum of the ejected exhaust gases. Conservation of angular momentum of rotating bodies is analogous to the conservation of linear momentum. Conservation of charge states that the total amount of electric charge in a system does not change with time. A capacitor, for example, becomes charged with equal amounts of opposite charge on its two plates. At a subatomic level, charged particles can be created, but always in pairs with positive and negative charge so that the total amount of charge always remains constant. In particle physics, other conservation laws apply to certain properties of nuclear particles, such as baryon number, lepton number, and strangeness. Such laws apply in addition to those of mass, energy, and momentum encountered in everyday life and may be thought of as analogous to the conservation of electric charge. See also symmetry. Management of natural resources Managing nonliving resources Soils Formation of soil Soils are the basis of support for most terrestrial life and a source of nutrients for freshwater and marine life. As noted above, soil is formed over time as the result of interaction between the living and the nonliving environmentclimate, organisms, and the physical surface of the Earth. Rocks are broken apart by the action of sunlight, wind, rain, snow, sleet, and ice. With the aid of wind and water movements as well as gravity, rock particles from high elevations are deposited on mountain slopes or in valleys, where they are further acted upon by the local climate, by plant and animal life, and by such other environmental factors as fire until they become soil. Nitrogen from the atmosphere, formed into nitrates by the action of lightning and atmospheric water vapour, may enter the soil with rainfall. Other nitrates may be added by the action of such living organisms as soil bacteria and various algae that can convert atmospheric nitrogen into the nitrates required for plant growth. These and other chemicals in the soil eventually become part of the living tissue in plants and animals. The chemicals are returned to the soil as organic wastes and litter that form humus, which is partly decomposed organic material. As humus continues to decompose, the chemicals within it enter the soil for further use by plants and animals. Soils vary from place to place depending upon the rocks and minerals from which they are derived, the nature of the local climate, and the kinds of organisms that live in or on them, as well as the amount of time that these factors have been operating. Developmental soilsi.e., those still being modified by climate and organismsreveal the nature of the parent materials from which they are derived; mature soils, those that have achieved a balance among the various forces operating on them, show in particular the influence of the climate and vegetation in which they develop. Soils also differ greatly in their inherent fertility and in their ability to support life. Those derived from quartz sand, for example, may be naturally deficient in calcium, magnesium, and other elements essential to plant growth. The surface layers of those soils developed in humid, forested regions are often heavily leached, as rainwater containing weak organic acids percolates through them and dissolves the more soluble minerals. Because soils are essential for such purposes as growing crops, forage, and timber, it is important that they not be allowed to wash or blow away more rapidly than they can be regenerated, that their mineral fertility not be exhausted, and that their physical structure remain suited to the continued production of desired plant materials. The objective of soil management, therefore, is to keep soil in place and in a state favourable to its highest possible productive capacity. Soil erosion In the past and, to a considerable degree even now, soils have not been managed effectively. Those exposed through cultivation to the erosive effects of wind have been blown away; those laid bare on sloping ground have been washed downhill by rainfall. Although soil erosion has long been recognized as a major conservation problem, erosion as suchand its converse, the deposition of eroded soil particlesis not a problem but a normal and natural process leading to both soil development and maintenance. Soils exist only because of past erosion and deposition. The conservation problem involved in soil erosion is the accelerated erosion that occurs when soil cover in the form of living or dead plant material is removed. In such cases the soil then erodes at a rate faster than it can be replaced by normal deposition of particles on the soil surface or by the breakdown of rocks and minerals. In severe cases, such erosion leads to the formation of deep gullies that cut into the soil and then spread and grow until all the soil is removed from the sloping ground. Under severe wind action, the finer particles of surface soil are blown away and form drifts and dunes, leaving only the coarser sands and gravels on the soil surface. Although measures to stop soil erosion are now used in most technologically advanced countries, the problem remains a major one. It is particularly severe in the tropics, where high rainfall and steeply sloping ground favour the rapid loss of any soil exposed by agriculture, and around the edges of the world's deserts, where destruction of natural plant cover by cultivation or livestock grazing causes soil loss through wind action and the spread of desert-like conditions. To prevent wind erosion, shelter belts of trees have been planted to break the force of the wind. The practice of covering soils with plant litter (mulch) when they are not actually covered with growing plants also helps to hold them in place. Cultivating at right angles to the direction of the wind further serves to prevent wind erosion. Water erosion on sloping ground may be prevented by terracing on steep slopes or by contour cultivation on gentler slopes. In the latter a slope is plowed along horizontal lines of equal elevation. Strip-cropping, in which a close-growing crop is alternated with one that leaves a considerable amount of exposed ground, is another technique for reducing water erosion; the soil washed from the bare areas is held by the closer growing vegetation. In the tropics maintaining a tree shelter over the ground serves as a means for breaking the force of raindrops, thus reducing their erosive power, and also to screen out direct sunlight. In addition to causing damage to certain crops, sunlight can accelerate the breakdown of organic materials in the soil at a rate that is faster than is desirable. The history of conservation Early practices For most of its history, the human species has lived by hunting animals and gathering wild plant foods. By extrapolation from studies of peoples who today live by such methods, it can be suggested that the relationship of hunter-gatherers with nature was relatively benign. It can also be suggested that people acquire and pass on through oral tradition a remarkable amount of knowledge about the plants and animals with which they associate and on which they depend. A number of breakthroughs in modern medicine, for example, have come from observing the therapeutic uses that traditional tribal cultures make of various wild plants. It is also known, however, that in prehistoric times people did modify their natural environment. Many grassland areas throughout the world have come to exist because people used fire as an aid to hunting or to modify vegetation to make it more suitable to their needs. Early hunting and gathering cultures contributed to the extermination of some animal species, although this seems to have been more of an exception than a general practice. For the most part, early humanity lived in an equable balance with the natural environment, if for no other reason than necessity. If they had done serious damage, people could not have survived. Agriculture has been practiced only during the last 10,00012,000 years, and urban civilization has been in existence only during the last 6,000 years. With urban life came pressure upon the natural environment and upon agricultural lands that was sometimes excessive. In the Asian homelands of Western agriculture there is widespread evidence of serious soil erosion during ancient times. Destruction of vegetation and the spread of deserts followed the rise of early urban civilizations in many areas of the Middle East and North Africa. Ancient conservation practices Certain conservation practices did develop in early civilizations, however. Some species of animals were protected by religious taboos; religious sanctions prevented the destruction of forest groves and sacred mountains. The use of organic fertilizer to maintain soil fertility is found among many more recent primitive peoples and has had a long history in Western agriculture. The Bible is filled with various injunctions governing the use of land and resources that have a conservation function. Civilizations such as those of the Phoenicians and the Incas developed sophisticated techniques of terracing to prevent soil erosion on hillsides and to make more effective use of water for irrigation. The earliest civilizations also show evidence of the creation of reserves or parks to protect wildlife or natural areas. Although they were hunting preserves for the use of royalty, they also served a conservation function. As civilization developed, the accumulation of human experience led to increasingly sound land-use practices, evidence of which is found in the written descriptions of Roman agriculture and, later, in the well-tended irrigated fields and gardens developed during the height of Muslim culture. The agricultural landscapes of preindustrial western Europe, Japan, and China reflected great skill in the conservation of soil resources. Irrigated lands in the Nile Valley and volcanic soils in tropical Southeast Asia have been kept fertile and productive over thousands of years. In preindustrial times, however, concern over wild nature was not widespread, largely because it was viewed as vast and inexhaustible relative to the domain, the numbers, and the power of human beings. This view was a justifiable one, because the 500,000,000 people who inhabited the world in 1600 lacked the energy sources and the machinery to effect great environmental changes. Moreover, most of the Earth's surface was sparsely settled. Types of natural resources In classifying natural resources it has been traditional to distinguish between those that are renewable and those that are nonrenewable. The former were once considered to be the living resourcese.g., forests, wildlife, and the likebecause of their ability to regenerate through reproduction. The latter were considered to be nonliving mineral or fuel resources, which, once used, did not replace themselves. In practice this separation is not entirely satisfactory, for reasons that will be dealt with in a later section. There are, nevertheless, certain aspects of conservation that apply specifically to nonliving resources: 1. Beneficiation is the upgrading of a resource that was once too uneconomical to develop. It usually depends upon technological improvements, such as those that make possible the concentration of a dispersed fuel or mineral so that it can be more easily handled, transported, or processed. 2. Maximization is the aggregate of those measures that avoid waste and increase the production of a resource. 3. Substitution involves the use of common resources in place of rare ones, as, for example, the use of aluminum in place of less abundant copper for a variety of products. 4. Allocation is the determination of the most appropriate use for a resource and the assignment of the resource to that purpose. In market economies allocation is usually controlled by the pricing mechanism: if the demand for a particular purpose is high, then the price of a resource to be used for that purpose will also be high; this high price will in turn make it more likely that the resource will be used mostly for that purpose. In government-controlled economies a resource may be reserved only for what are considered to be its most important uses. 5. Recycling, one of the most promising methods for conservation of mineral resources, involves the concentration of used or waste materials, their reprocessing (if this is required), and their subsequent reutilization in place of new materials. If carried out in an organized and consistent manner, recycling can greatly reduce the drain on supplies of minerals. It is also appropriate for products derived from living resources, such as the reuse of wood and paper as well as the reclamation of organic fertilizers from sewage. Because all natural resources form a continuum, from those that are most renewable in the short term to those that are least renewable, they do not readily lend themselves to a single system of classification. It is useful, therefore, to examine the various types of natural resources in relation to their cycling time; i.e., the length of time required to replace a given quantity of a resource that has been utilized with an equivalent quantity in a similarly useful form. From this point of view, renewable resources can be considered as those with short cycling times and nonrenewable resources as those with very long cycling times. Any resource can be nonrenewable, however, if the demand and rate of utilization exceed its cycling capacity. Two kinds of natural resources, pasture grass and coal, can be used to illustrate the concept of cycling time. When grass is grazed by livestock or mowed, a crop of it is removed. If provision is made to protect the fertility and structure of the soil and to leave enough seed or adequate roots and vegetative parts to produce new growth, then a grass crop can be removed from a pasture each year for an indefinite period of time. Removal of one year's crop does not diminish the supply available for the next year if the land is cared for properly. The cycling time for this resource may be one year in areas in which climate limits growth, or it may be less than a year if growth can be continuous. By contrast, the coal resources of the Earth were built up over millions of years. Most were laid down during the Carboniferous Period of geologic time (from 345,000,000 to 280,000,000 years ago), when climates were warm. Extensive swamp forests covered large areas of the Earth, and conditions were favourable for plant debris to accumulate in extensive deposits without decomposing and breaking down organically. Subsequently, heat and pressure generated by the deposition of other materials on top of the organic debris and by movements of the Earth's crust transformed the plant remains into coal. Organic debris is still being produced in swamps and marshes, and over millions of years this, too, could become transformed into coal. The time scale is so great, however, that, for human purposes, coal can be considered as a nonrenewable resource. Thus, only the supplies presently available in the Earth's crust can be counted on for future use. Renewable resources Plants and animals The most clearly recognizable renewable resources are those consisting of, or produced by, living things. Agricultural crops, animal forage, forest crops, wild and domestic animalsall can continue to reproduce and regenerate their populations as long as environmental conditions remain favourable and an adequate seed source or breeding stock is maintained. Moreover, all can be cropped or harvested without diminishing their supply, provided that the cropping does not exceed the reproduction or growth rate. If it does, the resources will be depleted; and, if the rate of cropping continuously exceeds the rate of replacement or regrowth, the resource ceases to be renewable, and the species involved are reduced to the point of extinction. A renewable resource thus can be said to be minedthat is, it is removed at a rate that does not permit renewal. The renewability of a living resource is further endangered if the environment required by that resource is allowed to deteriorate or disappear. Sheep in a mountain pasture are a renewable resource only as long as the pasture produces vegetation that will nourish and support the sheep. If the pasture is overgrazed, the vegetation destroyed, and the soil eroded, sheep cease to be a renewable resource in that locality.